Early detection of disease is of utmost importance in improving the odds of successful treatment. However, once a patient presents with disease symptoms, often, the disease is somewhat advanced or established. In order to truly discover a potential problem at earlier stages, asymptomatic patients should be screened for early signs of disease.
Glaucoma and other ocular and nerve-related diseases are among diseases that could potentially be detected at an early stage. There exists in the art a variety of tests that are capable of detecting early onset of glaucoma and other diseases of the nervous system.
Pattern VEP is a well-known diagnostic aid in the detection of glaucoma and other nerve-related diseases. In this test, a patient observes reversing patterns displayed on a screen and such sensory stimulation of the visual field causes Visually Evoked Potentials (VEPs). Electrodes placed on a subject's scalp detect the VEPs.
In diagnosing and/or screening patients using VEP techniques, a clinician looks for an N75 P100 N135 complex in a resultant waveform. The N75 P100 N135 complex conveys important information about the condition of the nervous cells carrying a nerve impulse.
Pattern Electroretinography (PERG) is a diagnostic tool for ocular disease that is similar to VEP. However, unlike with VEP where signal from the visual cortex is captured at the back of the skull, with PERG signal is collected directly from the retina by way of a sensor placed under the patient's eye. With PERG testing the diagnostically important waveform has an N35-P50-N95 complex.
Typically, each time a pattern displayed on the screen is flipped, a signal is generated. After a specified number of signals is captured, a software program signal averages the plurality of captured signals and produces one waveform which represents the N75 P100 N135 complex or the N35-P50-N95 complex—as the case may be.
One problem with this method of producing a signal-averaged signal is that signals that do not correspond to the N75 P100 N135 complex or to the N35-P50-N95 complex may be included in the signal-averaged waveform. For example, signal artifacts caused by a patient blinking or moving may be erroneously included into the signal-averaged waveform. As a consequence, the sensitivity and specificity of the VEP or PERG test may be diminished or compromised.